The present invention is directed to methods for making or manufacturing an electrical device and the process, composition, and product thereof. More particularly, the present invention involves such multilayer electrical devices as-circuit boards constructed by joining a dielectric material to a subsequently applied conductive material. Still more particularly, the present invention involves an electrical device having a substrate or base, an applied dielectric material thereon, which in turn has a thin conductive coating thereon, and a conductive layer formed upon the conductive coating, the conductive layer being joined to the applied dielectric material in an improved manner.
Multilayer electrical devicesxe2x80x94those made from layering a dielectric material and a conductive material on a basexe2x80x94suffer from delamination, blistering, and other reliability problems. This is particularly true when the laminates are subjected to thermal stress.
Known attempts to solve these problems seem to have focused on physical or chemical roughening, particularly of the base or substrate. See for example, U.S. Pat. No. 4,948,707. Although oxide-related chemical roughening processes have been used, an emphasis on physical roughening may reflect the use of materials that are relatively chemically resistant. Both physical and chemical roughening approaches have improved adherence to the base.
However, the extent to which this adherence can be increased by roughening has its limits. And despite a long standing recognition of delamination, blistering, and reliability problems, and the attempts to find a solution, these problems have been persistent in electrical devices made of layered materials.
The inventors herein have observed that the general problem of poor adherence between the laminates or layers can be addressed by forming a unique surface structure, which is particularly suitable for joining the dielectric material to the conductive coating and conductive layer. The surface structure is comprised of teeth that are preferably angled or hooked like fangs or canine teeth to enable one layer to mechanically grip a second layer.
In comparison with the above-mentioned roughening techniques of the prior art, it is believed that a surface of the teeth is an improvement in that there is an increase in surface area. However, it is still better to use teeth that are fang-shaped to enable a mechanical grip that functions in a different manner than adherence by means of increased surface area. By using the fanged, angled, canine, or otherwise hooked teeth (in addition to increased to surface area), there is a multidirectional, three dimensional interlacing or overlapping of layers. For example, in joining the dielectric material to the conductive coating and metal layer, the conductive coating and metal layer is actually burrowed in and under the dielectric material and vice versa. Thus, separating them hot only involves breaking the surface area adherence, but also involves destroying the integrity of at least one of the layers by ripping the teeth, the layer pierced by them, or both.
Further, it has been found preferable to have numerous teeth sized and shaped so that they are not too large or too small. If the teeth are too small, wide, straight, and shallow, then the surface resembles the roughened surface of prior art techniques, vaguely analogous to a surface of molar teeth, and the adherence is not much better than that achieved by known prior art roughening techniques.
However, if the teeth are too large, deep, and fanged or hook-shaped, the teeth undercut the surface to such an extent that the strength of the dielectric material surface is weakened. As a result, adherence is decreased over the preferred embodiment.
Not too great and not too slight, the right sized and shaped teeth, set in a fanged orientation and with sufficient frequency, have been found to be the best structure. If the correct balance of these critically important factors is created, the result is a greatly improved circuit board or other such electrical device.
It is theorized by the inventors that the best methods for producing the teeth is to use non-homogeneous materials and/or techniques. For example, a dielectric material can have a non-homogeneous composition or thickness to bring about an uneven chemical resistance, such that slowed and/or repeated etching will form teeth instead of a uniform etch.